1. Field of the Invention
This invention relates to a reinforced corner structure for cloth, and more particularly to that type of reinforced corner structure fitted in cloth without stitching for facilitating production automation and reducing working time.
2. Description of the Prior Art
Cloth is usually woven with warp and weft. In order to avoid raveling at cloth corners, a reinforced stitched portion along the adjacent edges of a cloth corner is often required. This is particularly true for plastic cloth and canvas used for many tents and covers, of which the corner edges 1 and 2, as shown in FIG. 1, are always folded over and stitched thereat with an opening 3 provided in the corner and a grommet 4 fixed therein for allowing a cord to be inserted into the grommet 4 and tied at a support. However, as the opening 3 mars the warp and weft structure of the cloth, when the grommet 4 is subjected to pull and drag force, the periphery of the opening 3 will become ravelled and eventually break loose, causing the grommet 4 to come out from the opening 3. In order to overcome the above-mentioned shortcoming, some manufacturers have made an effort to inset a side string 5 along the adjacent cloth edges 1 and 2 for increasing the tensile strength of the cloth edges 1 and 2. However, owing to the different ways of tying the cord, the opening 3 of the cloth will be damaged. If the cord 6 is tied as a square knot, as shown in FIG. 2A, with two portions of the cord 6 respectively kept in close engagement with the side string 5 at two sides 1 and 2, when the cord 6 is tightened, the tensile pull of the cord 6 will be evenly provided by the two portions of the cord 6 at both sides 1 and 2 of the cloth; thus, the strain suffered by both the opening 3 and the grommet 4 can be decreased. However, if the cord 6 is tied in any simple knot, as it is often done by some careless people, with the cord 6 looped at either one side or at the center of the corner of the cloth as shown in FIG. 2B, when the cord 6 is tightened, the tensile pull of the cord 6 will be completely absorbed by both the opening 3 and the grommet 4, so that the latter may easily be damaged and come off form the cloth. For alleviating the effects of the above-said defect, some manufacturers have stitched a triangular cloth piece 7 at the cloth corner, as shown in FIG. 1, for reinforcing the area where the grommet 4 is fixed in the opening 3. Nevertheless, the stitching operation of the triangular cloth piece in cloth, particularly for the bulky plastic cloth and canvas used for tents and covers is rather troublesome because not only is the side folding operation for a bulky weight cloth difficult, but also an additional two or three assistants are needed to help the sewing operator in moving the cloth during stitching, especially in turning at the cloth corner. In addition to the above-noted problem, as the reinforced triangular cloth piece 7 has to be aligned with the cloth corner, adjustment must be constantly made while stitching, wasting time in the stitching work. Despite the reinforced triangular cloth piece 7, if the cord 6 is tied in a single knot as shown in FIG. 2B, damage of the opening 3 and loosening of the gromment 4 will surely occur. At present, although further improvement has been tried to bond together the reinforced triangular cloth piece and the folded edges of the cloth through thermo-pressure bonding opration instead of traditional stitching, this improvement also encounters a serious problem; i.e. the total thickness of the bulky layers to be bonded by thermo-pressure bonding. The folded edges of the cloth are of a certain thickness, which together with the reinforced triangular cloth piece, formed of a folded square cloth piece, makes the total thickness exceed the bonding capability of a high-frequency bonding machine or other thermo-pressure bonding machine. On the other hand, if the corner edges of the plastic cloth or canvas are bonded through high-frequency or thermo-pressure bonding without the reinforced triangular cloth piece (to avoid excessive thickness), the cloth corner and the cloth surface are easily damaged as noted hereinbefore.